The present invention relates to a brake assembly for a vehicle having a fluid suspension wherein a brake signal operates a brake cylinder of the vehicle. A proportioning valve, having its load responsive element disabled and being responsive to the brake signal, provides a proportioned brake signal to the brake cylinder. A switch, responsive to an air spring pressure signal selectively connects the brake signal to the brake cylinder. The present invention further relates to a method for retrofitting a brake system by disabling the load sensing element of a proportioning valve and inserting a switch in parallel with the proportioning valve.
In a rail brake system, a control valve monitors brake pipe pressure and supplies pressure to or removes pressure from a brake cylinder in response to a change in pressure in the brake pipe. The brake signal from the control valve usually flows through a proportioning valve which has some sort of load sensing device that either detects that a rail car is loaded or not (the load indication is either xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d) or detects the degree to which the car is loaded (the indication is xe2x80x9cvariablexe2x80x9d).
There are generally two types of rail vehicle braking systems that sense and use the load in each vehicle or car of a train to adjust the amount of brake pressure applied to each car""s brakes. The first type utilizes a load sensing lever or similar mechanical device that is external but integral to an empty/load device, as illustrated, for example, in U.S. Pat. No. 5,211,450 (1993) to Gayfer et al, which is herein incorporated by reference. The movement of the load sensing lever, coupled with the resulting piston action of the valve affects and determines the value of the brake signal that is sent to the brake cylinder. The problem with this type of mechanical sensing device is that when a rail car has a self-leveling mechanism installed, there is no change in the relative position of the car body to the truck assembly supporting the car body. Thus, this type of empty/load device will not sense a change in the actual loading of the car.
A second type of braking system also has a sensing mechanism that is integral to, in this instance, an empty/load variable proportioning valve. In this case, however, the pressure reading from an external air spring is fed directly into the proportioning valve which then uses the amount of load in the car to help determine the value or proportion of the brake signal that is applied to the brake cylinder. This principle is reflected on U.S. Pat. No. 4,421,360 (1983) to Newton and in U.S. Pat. No. 3,910,639 (1975) to Engle. Engle has its applicability restricted mainly to light rail or mass transit use on trains with a limited number of cars. Newton focuses on a system relating to the combined transportation of highway and rail vehicles.
The present invention is designed for applicability to all types of rail vehicles including transit, freight and highway/rail.
The present invention provides a brake assembly comprising a switch and a proportioning valve connected in parallel.
The switch part of the assembly could, if desired, comprise a pressure sensor port for receiving a pressure signal from the air spring. The switch also could have an input port for receiving a brake signal from the control valve and a brake cylinder port for sending the brake signal to the brake cylinder. The switch could also have a spring that is responsive to air spring pressure that causes the switch to connect or disconnect the switch""s input port to its brake cylinder port. That connection occurs when the pressure signal from the air spring reflects a loaded car condition with the pressure signal possibly having a value in the range of at least 35-40 psi. If the value of the brake signal is less than 35 psi, the switch would be in the empty position and would not connect the switch""s input port to its brake cylinder port.
The second part of the assembly is a proportioning valve, which is well known in the art. It could, if desired, comprise a control valve input port to receive a brake signal from the control valve. It also could have a brake cylinder output port to send a proportional brake signal to the brake cylinder. The proportioning valve, if equipped with a mechanical load bearing sensing element, such as a lever, has it disabled. When disabled, the proportioning valve is not sensitive to the rail car""s load and thus proportions the brake signal it receives solely based on the value of that brake signal. The proportioning valve receives a brake signal from the control valve when the switch is in the empty position.
The device then sends a proportional brake signal from the brake cylinder output port to the brake cylinder.
This assembly can, if desired, be used as part of an overall rail car brake system by connecting the inventive assembly with a control valve, a brake cylinder and an air spring. The air spring provides a pressure signal that is used by the switch to determine whether or not a brake signal from the control valve will flow through the switch unproportioned to the brake cylinder.
The inventive brake system""s switch and proportioning valve, supra, are comprised and function as previously described in the inventive brake assembly description above.
The brake system""s control valve provides the brake signal that is sent to the brake cylinder either through the switch (when it is in the xe2x80x9cloadedxe2x80x9d position) or through the proportioning valve (when the switch is in the xe2x80x9cemptyxe2x80x9d position).
An air spring, which can be a self-leveling support for the rail car, provides a pressure signal to the switch. When the pressure signal has a value in the range of at least 35-40 psi, the switch will move to the xe2x80x9cloadedxe2x80x9d position and the brake signal will flow through the switch directly to the brake cylinder. Otherwise, the brake signal flows through the proportioning valve to the brake cylinder.
The present invention could be utilized for retrofitting a proportional brake system and comprises the steps of: first, disabling the load sensing element of the proportioning valve; and second, inserting a switch in parallel between the control valve input port and the brake cylinder outport port of the system""s proportioning valve. The switch is responsive to a pressure signal from an air spring that is part of the rail car""s support system and also provides an empty/load brake system input. The switch is responsive to selected values of the pressure signal from the air spring to selectively connect a brake signal at its input port to its brake cylinder port thereby providing the brake signal to the system""s brake cylinder.
The switch can, if desired, connect the brake signal to the brake cylinder when the pressure signal has a value in the range of at least 35-40 psi.
Other aspects of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.